Before this commit, the content that were swapped by an extension via
`handleSwap` was not handled by htmx: elemtents with `hx-` attributes,
scripts, no `load.htmx` event...
With this commit, if the `handleSwap` command returns an array of newly
added elements (only the first level), then they will be handled by htmx
like it's done for internal swap.
To not break existing extensions, `handleSwap` can still return `true`
to tell that the swap was handled, assuming than there is no new
elements to handle.
A new test was added with a button that, when clicked, loads a text and
a span with `hx-trigger=load`, both handled by an extension. This commit
allows this span to be loaded.
The return of the `morphdom-swap` extension was updated to return the
target element, even if unchanged, to let htmx check in the maybe new
content that there is something new to handle. This is tested in a new
test.
If an element is replaced by an extension in `handleSwap`, the events
(`afterSwap.htmx` and `afterSettle.htmx`) were not received by the
`onLoad` method of extensions defined on parents of the target, because
theses extensions were retrieved after the replacement, and so it was
not possible to get through the parents, the target not being in the dom
anymore.
This commits loads the extensions for the target and save them in
`eventDetail` before doing the swap, so they are accessible in
`triggerEvent`, and passed to `withExtensions` that use this list if
passed (else load them).
A new test is added that fails without the updates in `htmx.js`.
